The invention relates to a sheet guiding device for printing presses having guide surface members with slit nozzles for receiving and transmitting blast air. The slit nozzles are aimed in a direction crosswise to a sheet travel path.
A sheet guiding device of this general type has become known heretofore from the published German Patent Document DE 34 11 029 C2. In this known sheet guiding device, an attempt has been made to achieve a reliable floating or suspended guidance of the sheets by using nozzles having different blowing directions. A floating sheet guidance device must be used during two-sided printing to avoid smearing of the ink along the guide faces, however, it has disadvantages. It is either difficult or not at all possible to obtain a floating guidance for unstable sheets, especially sheets with low weight or a low density (less than 100 g/m2). Additional problems arise at high machine speeds due to arising centrifugal forces which make clean sheet guidance via the floating guide difficult.
It is accordingly an object of the invention to provide a sheet guiding device for printing presses which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type, and which provides a floating guiding device which can process sheets with a low weight and/or a low density (less than 100 /m2).
With the foregoing and other objects in view there is provided, in accordance with the invention, a sheet guiding device for a printing press, having guide surface members with slit nozzles for emitting blast air, the slit nozzles are aimed in a direction to an outside of (crosswise to) a sheet travel path.
In accordance with an added feature of the invention, the slit nozzles have an air blowing direction and the air blowing direction is essentially perpendicular to the sheet travel path.
In accordance with another feature of the invention, the guide surface members have an area and the area is occupied by a different degree of concentration of the nozzles to suit the particular air requirement for keeping sheets taunt.
A further feature provides that the guide surface members be arrayed with a varying number of nozzles or a varying density thereof per unit area to suit or match the particular air requirement for keeping the sheets taunt. For example, it is thus possible for the entry and exit regions of the guide surface members to be provided with a greater density of nozzles per unit area or a higher degree of occupancy by nozzles in the respective area, while the guide zone(s) located between those regions have a lower nozzle density or degree of occupancy per unit area. It is also possible for the nozzle density or degree of areal occupancy to be provided greatest in the middle of the sheet travel path and to decrease toward the edge or sides thereof. This is especially expedient if the nozzles are slit nozzles directed towards the outside of the sheet travel path. Then, the corresponding air flow is generated in the middle of the sheet travel path and need merely be maintained towards the edge; that is, as many nozzles as in the middle of the sheet travel path are no longer needed.
In accordance with an additional feature of the invention, there are axial fans and/or adjustable-speed fans for supplying air to the slit nozzles. The air supply to the nozzles is preferably accomplished via the adjustable-speed fans. In this manner, in the blowing or blast mode, the floating or suspension guidance can be adjusted.
In accordance with yet another added feature of the invention, there are air supply chests for effecting a supply of air to the slit nozzles.
In accordance with yet another feature of the invention, there is an axial fan assigned to each of the air supply chests.
In accordance with another additional feature of the invention, the slit nozzles are stamped into the guide surface members.
In accordance with a concomitant feature of the invention there is a central air supply provided with blowing air for supplying air to the slit nozzles.
It is possible to have the desired air act upon relatively large nozzles individually by the fans, or an air supply can be provided wherein individual regions or portions of the air supply are made effective via air supply chests or boxes, to each of which an air supply is assigned. Naturally, a further subdivision is also possible, depending upon how strong the action of the air in a certain region is required. The advantage of the air supply chests or boxes is that many nozzles can be supplied by one air supply element. For a relatively large number of nozzles, for example, correspondingly strong axial fans can be used. Due to the subdivision, it is nevertheless possible to supply air variably to the individual regions. It is therefore proposed that an axial fan be assigned to each blower chest, and that the size of the air supply chests be adapted to the air requirement of the respective region.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a sheet guiding device for printing presses, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.